Tuesday, November 8, 2011

Breasthook, Quarter Knees, & Gunwales

Quarter Knees and Breasthook

Forewarning to aspiring boatwrights: Numerous complicated elements exist within this apparently innocuous phase. Thankfully, the challenges of this process are counteracted by the sheer aesthetic euphoria invariably resultant from proper completion.

To complement the interior frames, the quarter knees and breasthook were fashioned from identical stock (white oak).  Whether an individual starts with either the quarter knees or the breasthook does not appear to perceptibly influence the final result, as each approach entails formation of progressive, differentiable (a reference intended for the mathematically inclined) curvatures of natural aesthetic nature.  Within our context, this morphology formulation was executed completely by visual instinct (employing the "if it appears correct, it is" adage).  To commence, preliminary templates were fashioned from spruce before committing the finalized contours to oak.  Predominantly, the curves for the quarter knees were inscribed freehand whereas on the breasthook the center portion of the curve was circumscribed with a trammel to ensure consistency, although the remaining portions accommodating convergence of this arc fluidly with the inside gunwale edge was completed unassisted.

Optimally, these structurally augmenting members possess grain orientation perpendicular to predominating tensile shear forces, as material resilience is maximal within this axis. Traditionally, artisans employed specifically-obtained natural "crooks" derived from buttress roots or the confluence of a lateral branch with the primary trunk, as the lignin fibers contained therein intrinsically conform to required curvatures. However, the conspicuous absence of conducive natural stock was surmounted through usage of an alternative, modernized technique.

Profoundly appreciating the convienience afforded by sophisticated polymer adhesives for the nth instance within construction, we elected to form each of these interior finishings out of two distinct pieces unified at contact by epoxy and a couple of associated tenons, acquiring the rarified perpendicular configuration of grain to stress imposition we sought to achieve. As depicted below, the resultant component entailed two constituents, exhibiting a neat acute angle between the respective pieces.  For the breasthook, an assistive jig was constructed to immobilize the unfinished piece unwaveringly, permitting impartment of the center curve via a trammel and router arrangement to attain circularity.  Although bandsaws are typically utilized to address extensively non-linear cuts, the absence of this (routinely indispensable) item within our shop catalyzed additional extemporaneous improvisation to address matters, ultimately yielding a functional alternative: enlistment of a hand held jigsaw in conjunction with a supportive apparatus to achieve commenurable outcomes.

Succeeding this, we had to deviate from familiar theoretical domains of arc-lengths, radii, and angular computations, commencing the daunting process of reconciling intangible theory with physical reality. This daunting task--entailing incremental, subjective fitting and gradual alteration--was repetitive, but yielded continual positive encouragement as the realized and intended forms progressively converged to congruity. For the breasthook, the first task entails hand cut excision of the center portion that will ultimately accommodate the stem.  We performed this by inserting the breasthook into place (coaxing it as far forward as feasible) and then scribing the position of the stem's extremities onto the breasthook using a straight rule.  Then, by transferring the depth of the stem (measured) and drawn across the two outside lines squarely, we obtained a reasonable representation of the stem's outline.  Once this excess portion was eliminated, we started the process of manually trimming the angles of the sides to match the planks, as the hull's contours produce a compound angle and minute curvature that change as a function of precise position, defying the usage of mechanized techniques.  Succeeding extensive trial and fitting, we achieved sufficient breasthook-hull congruity to placate our intrinsic propensities towards aesthetic perfection.

With this shape defined, the next step encompassed elimination of surplus material to facilitate overlap for where the gunwale would rest.  Again, this initially exhibited a deceiving simplicity that belied its true attributes.  Intrinsically, there exist two factors collectively influencing matters within this element: correspondent incision depth is salient to ensure a smooth transition as the curve progresses naturally into the gunwale component, and the perpetual, inevasible notion of angle contemplation to facilitate congruency within contact surfaces.  These aspects of function and associated implications were prognosticated upon considerably preceding the execution of irreversible cuts and angles.  Conclusively, we ascertained that the plank incantation should be maintained such that the cut ran parallel to the planking.

The knees proved to be much easier to fit as the back of the boat is mainly square and the planks are more upright than at the front.  The process was essentially comparable to that employed for the breasthook--albeit appreciably expedited!

Once the pieces were satisfactorily addressed, they were subsequently counterbored and definitively anchored with a couple of stainless steel screws on each side.  The obstruction of these persistent voids will transpire at a future juncture.


Superficially analyzed, fitting the gunwales seemed relatively straightforward. We took the gunwale (two pieces of oak were scarfed and glued up with epoxy to create a long board) and imposed a progressive taper (about half the thickness of the gunwale) at both extrema to alleviate the ocular abruptness of member truncation and impart aesthetic fluidity. Subsequently, we clamped one end onto the shear strake just short of the stem and transferred the angle of the stem on to the gunwale through utilization of a small piece of wood, estimating the approximate angle through the thickness of the gunwale. We then cut both angles and checked the fit of the gunwale, made slight alterations, and then proceeded to clamp the outer gunwale along the length of the boat, acknowledging that the extra length that protruded beyond the transom would be easy to cut off with a handsaw once the gunwales were all completed.

In effectual dichotomy to its exterior counterpart, inwale conception constitutes a redoubtable prospect!  Innately instransigent within linear rigidity, this structural oak component tenaciously resisted numerous valiant attempts to forcibly impose morphological congruency, generating resultant consternation. In conjunction, implications arose from origins within the inflexibility of gunwale elements, as the inherent immalleable resistivity impeded efficacious measurement and trial insertion. Emergent hesitation catalyzed by cognizance of such notions was subsequently exacerbated by a suffusive consciousness of aesthetic prominence ascribed to these boat constituents upon predication of evident visibility.

Consequently, a rational prudence and circumspection characterized our general approach to inwale confrontment, entailing a progressive truncation protocol to incrementally abbreviate an initially-excessive length to hull correspondence. Demonstrating an atypically blas√© confidence attributable to rarified perceptions of process infallability, the gradualized advancement commenced: eliminate a near-indiscernible quantity of wood, analyze length comparatively with existent dimensions, repeat tautologically. Inauspiciously, however, a minute threshold appears to differentiate between length acuity (permitting successful insertion) and excessive shortness (a concept manifest within our initial attempt, wherein we were about a 1/4" short and experienced the elicitment of unbridled, indignant expressions!!!!)  Fortuitiously, marginal craft asymmetry generated sufficient differentiation between the proportionality of repective lateral polarities, permitting utilization of the initial member within the alternative location.  Evidently, the didactic lesson portrayed within this salvaged debacle indicates the salience of executing construction within a descending magnitude fashion to facilitate employment of erred stock within functional surrogate capacities. However, retrospective analysis affirms the ideality of a tertiary approach: composing an emulative gunwale from inexpensive stock  to obtain optimal dimensions preceding transferrence to consequential material, as this proposition minimizes inherent risk and yields incomparable expediency. Indisputably, the first-time nature of this construction attempt invokes affliction with tribulations evaded by inveterate participants, but our intrinsic ebullience persists undaunted.

Once the two gunwales fabricated and conducively situated, the subsequent component necessitated within progressive advencement comprised integration of the structurally-supportive blocking elements that reinforce the internal gunwale. Despite our prevailing orientation towards retention of accordance with specified dimensional and design aspects adumbrated within Atkin's templates, subjective aversion to the visual appearance of prescribed blocking configurations stimulated an election to deviate from the intended arrangement. The books on many matters concerning boat building are missing the many details that the amateur builder invariably deliberates extensively upon: "Should the blocks retain invariant magnitude while interim voids differ in proportions, or vice-versa?" , and "What effective approach to distinct inter-frame spacing should be utilized to maintain visual appeal?".  Succeeding appreciable analysis, tentative positioning, and conceptual visualization, a viable permutation of blocking attributes surfaced, encompassing a constant quantity of blocks within respective positions intervening between structural knees and marginal isolation magnitude alteration in compensatory accommodation for differing inter-frame dimensions.  In conjunction, conclusive decisive dictation entailed employment of square entities in contrast to archetypal canoe-indicative cambered blocks upon predication of traditionalism and subjective perceptions of pulchritude.

Once everything was decided upon it was a relatively straightforward task to counterbore and screw the inner and outer gunwales together and to screw the frames to the gunwales.

Still more adjustments

After getting everything into place we started looking at the gunwales and decided that the placement of the quarter knees and breast hook was slightly too low. So we elected to remove them and shift them up so that they are about a ¼” proud of the side planks and transom. This way we can plane/sand them down to create a nice rounded appearance. This work was straightforward and the extra holes we drilled to reposition them will be covered by the gunwales.

Although the advent of cold weather has compelled temporal aberration within construction, we intend to conclude interior components and execute finish application succeeding the emergence of springtime. Presuming the obligations associated with education/occupation are conducive to boat labor, the intentioned launch timeframe of May appears persistently feasible, generating substantial anticipation! 

Joe Lapstrake

1 comment:

  1. Loved your command of the English language.